Fix application credential doc example
Fix application credential doc example

In 532452f7 we converted the application credential examples to use
python-openstackclient instead of python-keystoneclient, but forgot to
update the prose to go along with it. Correct the client name now.

Change-Id: I6795e42ffc1e9134beedd5fa78d079dba4c5ef42

mahak/keystone,openstack/keystone,openstack/keystone,mahak/keystone,mahak/keystone,openstack/keystone